I have a LA, and I like to leave extra on the sides for my "test" stitching -- an area where I can calibrate the tension when I change threads or needles. Also, if you're asking for custom work with rulers, a wider backing makes it easier -- at least on my machine, the ruler base hits the side clamps if the sides are not very wide. I can "lift" the clamps up a bit with dowel rods, but it's a lot nicer when I don't have to do that.